For example, in the related art, a helium cooling high temperature gas cooled reactor disclosed in PTL 1 is a gas-cooled reactor that has helium gas as a coolant, in which a primary helium circuit including a nuclear reactor and a secondary helium circuit including an intermediate heat exchanger and a helium turbine are divided, heat in the primary helium circuit operates the helium turbine in the secondary helium circuit, and thus, electricity is generated.